The invention relates to a guard means for machines such as pressbrakes, guillotines, stamping machines and the like, in the case of which a first machine part performs working movements toward a second machine part, comprising at least one photoelectric detector, more especially a laser photoelectric detector, whose light beam extends perpendicularly to the direction of working movement and which is able to be so positioned between the two machine parts on one thereof that its light beam is at a safety distance from such machine part, such safety distance being able to be set by means of a guard means arranged adjustably on this one machine part, such guard means bearing the at least one photoelectric detector, a halting means adapted to arrest the working movement on interruption of the light beam and a switching off means for switching off the halting means directly prior to interruption of the light beam.
In the case of such a guard means disclosed in the German patent publication 19,717,299 A1 two photoelectric detectors or, respectively, two light beams are arranged one after the other in the direction of motion and the safety distance between them may be adjusted. For setting the distance the guard means is shifted toward this one machine part having the guard means, until the first light beam is interrupted by the machine part or, respectively, its tool. Then the safety distance is set. This arrangement however requires two photoelectric detectors or, respectively, light beams arranged one after the other in the direction of motion which constitute a substantial cost factor.
Although it is a known practice in an arrangement with a single photoelectric detector to apply a shim to manually set the distance from the one machine part or, respectively, its tool and to move until its light beam is interrupted by such shim, however for such adjustment two persons are required, more particularly in the case of extremely large machines, and the person holding the shim is exposed to substantial danger of injury by the tool.
Accordingly one object of the present invention is to provide a guard means of the initially described type with which there is no need for an additional adjustment photoelectric detector without this meaning that the safety distance of the guard means is not able to be set by a single operator or be set completely automatically.
In order to achieve these and/or other objects appearing from the present specification, claims and drawings, in the present invention means are provided for the performance of a first movement of the guard means as far as interruption of the light beam by the machine part bearing the guard means and the performance of a second movement of the guard means in the opposite direction, the displacement or distance traveled, which sets the safety distance, in the second movement being able to be predetermined by an electrical measuring and/or control means.
In accordance with an advantageous embodiment of the invention the safety distance is stored as the displacement of the second movement in the measuring and/or control means so that in a simple manner the guard means is moved in accordance with this electrically stored displacement in order to set the safety distance. There is no need for a second adjustment photoelectric detector and this means a substantial saving in costs. By presetting different stored values or by using calculated stored values it is possible for the safety distance to even be set in variable manner dependent on the respective requirements.
The measures indicated in the claims represent advantageous further developments and improvements in the guard means of the invention.
For the storage of the displacement setting or predetermining the safety distance the control means preferably comprises a data memory. For optimizing this data item it is an advantage to provide means for the automatic detection of overrun displacement of the moving machine part after a stop signal so that a value related to such overrun displacement predetermines the safety distance in the data memory. The safety distance may be so set in an optimum manner dependent on the respectively employed tool, the setup of the machine and other parameters such as service life, condition of the drive device and the brake device and the like.
In order to detect changes in condition it is useful to provide a comparison means for the comparison of the stored overrun displacement with a newly detected overrun displacement, means being provided for renewed automatic setting of the safety distance in a fashion dependent on the new overrun displacement, if a predeterminable departure between an earlier an a new overrun displacement is detected. The means for the automatic detection of the overrun displacement during the closing motion of the machine parts may preferably be activated after an interruption in the electrical power supply.
In order to improve safety several electrical control switches or wireless control elements, which are functionally connected with the moving guard means, may be provided, means also being provided for activating the closing movement of the machine parts only when a preselected control switch or a control element is reached. The same constitutes an additional safety measure in order to prevent a substantially too low setting of the safety distance in the case of there being an error in the automatic setting of the safety distance.
It is an advantage to provide an electric motor drive for causing, manually or completely automatically, the movement of the guard means during setting of the safety distance.
In order to increase the accuracy of adjustment the electrical measuring and/or control means comprises means for causing the setting of the displacement during the second movement only when interruption of the light beam has occurred, means being provided for activating the closing movement of the machine parts only on reaching a preselected control switch or control element.
Further advantageous developments and convenient forms of the invention will be understood from the following detailed descriptive disclosure of one embodiment thereof in conjunction with the accompanying drawings.